Recently, electromagnetic interference (EMI) and radiated emission has become a major problem for high-speed circuit and package designers, and it is likely to become even severe in the future. As circuitry and packages have become smaller and more sophisticated, more circuits and interconnection lines are being crowded into less space and operating with higher clock frequencies, thus increasing probability of electromagnetic radiated emission and interference. Small-integrated digital circuits and packages do not at first seem to be a serious source of radiated emission and interference. However, their higher switching speed, combined with inductance of the conductors that interconnect them, makes them a major source of radiated emission and interference. However, until recently, designers of integrated circuit and package did not give much consideration to electromagnetic radiated emission and interference in their designs. Power/ground bounce, fast out-put driver transition, transmission line reflection, and crosstalk are causing these radiation.
This paper reports the effects of on-chip and off-chip decoupling capacitors, output driver size, the proposed differential line scheme circuit, and on-chip electromagnetic radiated emission, with respect to electromagnetic interference.
Test ICs, packages and boards were designed and fabricated, which have different decoupling capacitors, output drivers and board layouts. Also different on-chip and off-chip antenna patterns were designed and fabricated. The antenna patterns include differential-mode and common-mode radiating structures, which could be possible layout of on-chip and board layouts. Test ICs were packaged using 64QFP. The radiated emission was measured using TEM cell, GTEM Cell, spectrum analyzer, oscilloscope.
This paper discussed the relation between IC design and EMI and proposed the circuit for EMI reduction. Specially, the design rule for optimized On-chip and Off-chip Decoupling Capacitors, the effect of output driver size on EMI, and the design rule for optimized output driver size were determined. A circuit using differential line scheme was proposed, which performed 10dB EMI reduction rather than the conventional scheme. It is verified that on-chip antenna effect on on-chip electromagnetic radiated emission can be ignored.
